Conventionally, in pattern inspection or the like of printed boards, there is a case where a method is employed which is adapted to inspect a board not entirely at a time but on a region-by-region basis, each region having a constant width extending laterally of the board, though whether or not to employ this method depends upon the sizes of boards. Specifically, a board being fed in on direction is exposed to band-like lighting along a line perpendicularly intersecting the feeding direction, and the images of flaws and the like present in an illuminated portion of the board are picked up one by one.
One known lighting system used for this type of application comprises a pair of elongate rectangular light-emitting members disposed to form a flared shape widening toward a board, the light-emitting members being adapted to light the region having a constant width to be illuminated obliquely from an upper forward side and an upper rearward side.
By the way, demand is growing for a higher board feeding speed with a view to, for example, shortening the inspection time to meet increasing volume production of products or the like and, hence, the lighting luminous intensity also needs to be enhanced with increasing feeding speed.
However, simply enhancing the luminous intensity of light emission itself is not preferable because it incurs upsizing of the lighting system and an increase in power consumption. Use of a lens for concentrating light emitted from the light-emitting members is easily conceivable. However, since each light-emitting member itself comprises a surface-emitting type light-emitting member having a certain width, the method of simply concentrating light requires a lens having a larger diameter, which may also incur upsizing of the lighting system and a rise in price.